Chronic Myelogenous Leukemia (CML) is a hematological disorder which constitutes about 15% of adult leukemias, characterized by the malignant expansion of the myeloid lineage. The genetic hallmark of CML is a reciprocal translocation between chromosomes 9 and 22 resulting in the so-called Philadelphia (Ph) chromosome. The molecular consequence of this inter-chromosomal exchange is the creation of the chimeric gene BCR-ABL, encoding a tyrosine kinase polypeptide in which the tyrosine kinase domain is constitutively activated. The expression of this fusion protein has been shown to be necessary and sufficient for the transformed phenotype of CML cells (FADERL, S, et al. The biology of chronic myeloid leukemia. New England Journal of Medicine. 1999, vol. 341, no. 3, p. 164-172. SAWYERS, C. Chronic myeloid leukemia. New England Journal of Medicine. 1999, vol. 340, no. 17, p. 1330-1340.) In addition to CML, deregulated ABL kinase activity resulting from the Ph chromosomal translocation is also detected in up to 20% of adult lymphoblastic leukemia (ALL) patients (OTTMANN, O. G., et al. A phase 2 study of imatinib in patients with relapsed or refractory Philadelphia chromosome-positive acute lymphoid leukemias. Blood. 2002, vol. 100, no. 6, p. 1965-1971.)
ABL transduces signals from cell-surface growth factor and adhesion receptors to regulate cytoskeleton structure. Many signalling proteins have been shown to interact with ABL which activate a range of signalling pathways. Therefore, inhibition of ABL constitutes a new approach to improve therapy for patients with CML.
The discovery that BCR-ABL is required for the pathogenesis of CML, and that the tyrosine kinase activity of ABL is essential for BCR-ABL-mediated transformation, made the ABL kinase an attractive target for therapeutic intervention. Imatinib (Gleevec®, also known as STI571, EP 564409 A) is an ATP-competitive inhibitor of BCR-ABL which potently inhibits its tyrosine kinase activity The high selectivity and efficacy of Imatinib are due to its ability to bind and block BCR-ABL in a catalytically inactive conformation of the enzyme. Preclinical and clinical studies have demonstrated the remarkable efficacy and high tolerability of Imatinib, which is now the first-line treatment for all newly diagnosed CML patients (DEININGER, M, et al. The development of imatinib as a therapeutic agent for chronic myeloid leukemia. Blood. 2005, vol. 105, no. 7, p. 2640-2653.) However, Imatinib is highly effective in early phases of the disease, whereas patients in the accelerated and blastic phase of CML, as well as those with Ph+ ALL, frequently develop Imatinib-resistance (DRUKER, B. J., et al. Activity of a specific inhibitor of the BCR-ABL tyrosine kinase in the blast crisis of chronic myeloid leukemia and acute lymphoblastic leukemia with the Philadelphia chromosome. New England Journal of Medicine. 2001, vol. 344, no. 14, p. 1038-1042. SAWYERS, C. L., et al. Imatinib induces hematologic and cytogenetic responses in patients with chronic myelogenous leukemia in myeloid blast crisis: results of a phase II study. Blood. 2002, vol. 99, no. 10, p. 3530-3539.) A major mechanism for Imatinib-resistance is the evolution of clones that have acquired point mutations within the tyrosine kinase catalytic domain of BCR-ABL and directly prevent or weaken the interaction with the inhibitor. While most of them induce structural changes that prevent the ABL kinase domain to adopt the closed, inactive conformation required for Imatinib binding (SHAH, N. P., et al. Mechanisms of resistance to STI571 in Philadelphia chromosome-associated leukemias. Oncogene. 2003, vol. 22, no. 47, p. 7389-7395.), some mutations, such as the Threonine 315 to Isoleucine substitution (hereinafter referred to as T315I), directly interfere with Imatinib interaction at the ATP binding pocket.
The understanding of the molecular basis of Imatinib resistance has stimulated the search for new BCR-ABL inhibitors that are effective against clinically observed imatinib-resistant ABL-mediated diseases. A number of second generation ATP-competitive inhibitors of BCR-ABL, such as AMN107 (WEISBERG, F, et al. Characterization of AMN107, a selective inhibitor of native and mutant Bcr-Abl. Cancer Cell. 2005, vol. 7, p. 129-141.) and BMS-354825 (also known as Desatinib) (SHAH, N. P., et al. Overriding imatinib resistance with a novel ABL kinase inhibitor. Science. 2004, vol. 305, no. 5682, p. 399-401.), have been developed and are now under evaluation in early clinical trials. These compounds are active against the majority of the Imatinib-resistant ABL mutants, but none of them is active against the T315I mutant, which is the second most frequent mutation occurring in Imatinib-resistance patients (O'HARE, T, et al. In vitro activity of Bcr-Abl inhibitors AMN107 and BMS-354825 against clinically relevant imatinib-resistant Abl kinase domain mutants. Cancer Research. 2005, vol. 65, no. 11, p. 4500-4505). It can be concluded that it is particularly difficult to inhibit the T315I ABL mutation with an ATP-competitive compound. As a matter of fact, until very recently the only inhibitor that has been reported to be active also against the T315I mutant was ON12380, which indeed is a substrate competitive (i.e. a non-ATP competitive) inhibitor (GUMIREDDY, K., et al. A non-ATP-competitive inhibitor of BCR-ABL overrides imatinib resistance. Proc. Natl. Acad. Sci. U.S.A. . 2005, vol. 102, no. 6, p. 1992-1997.).
Recently, two ATP-competitive molecules, VX-680 (HARRINGTON, E. A., et al. VX-680, a potent and selective small-molecule inhibitor of the Aurora kinases, suppresses tumor growth in vivo. Nature Medicine. 2004, vol. 10, no. 3, p. 262-267.) and BIRB-796 (PARGELLIS, C., et al. Inhibition of p38 MAP kinase by utilizing a novel allosteric binding site. Nat. Struct. Biol. 2002, vol. 9, no. 4, p. 268-272.) have been reported to be able to bind in vitro to the T315I mutated tyrosine kinase domain of ABL with low nanomolar Kd, but showed a low potency for inibition of T315I BCR-ABL in cells (CARTER, T. A., et al. Inhibition of drug-resistant mutants of ABL, KIT, and EGF receptor kinases. Proc. Natl. Acad. Sci. U.S.A. 2005, vol. 102, no. 31, p. 11011-11016).
At present, there are no effective kinase-targeted treatments for patients affected by Imatinib-resistant T315I ABL-mediated diseases, which are estimated to constitute 20% of all patients that relapse after imatinib treatment and are expected to be selected for by treatment with the next generation inhibitors mentioned above. This represents an unmet medical need for new potent ATP-competitive inhibitor of the T315I mutant of BCR-ABL. The present invention addresses this problem.